Key Technique Research For HF Burst Communication System Based On Bit-Interleaved Code Modulation

High frequcency (HF) communication is an important communication method, especially in military communication; this is attributed to its simplity, moderate cost, ability to provide near global connectivity without repeaters, beyond line-of-sight, and ease of proliferation. But with the development of modern high technolgy war, traditional HF communication is threatened by modern electronic countermeasures, so it is very useful to develop efficient anti-jamming measures in HF communicaiton. The object of this dissertation is to study the applicaiton of Bit interleave coded modulation (BICM) in HF communication and relevant key techniques based on the model of a new HF adaptive burst communication system (ABCS) proposed by academician Lu Jianxun in China Engineering Academy.At the beginning the dissertation introduced the new techniques in modern HF communication, and put emphasis on the introduction of ABCS, including its basic theories, main characters and advantages over traditional HF communication system. Then BICM and its applications in ABCS was discussed. The following items give the summarization of the main work:1. The modem scheme was realized. BICM is a bandwidth-efficient code technology which adds the diversity order. BICM was applied to ABCS in this dissertation. The LDPC coded BICM system, BICM-ID(BICM with iterative decoding) based on hard decision and BICM-ID based on soft decision was respectively implemented and the performance was analyzed and simulated, which applied the bases to the choice of modem scheme.2. The synchronization scheme was realized. Synchronization is a key of burst communication, which has an influence on the system performance. Our scheme performed timing recovery and carrier recovery and we put the emphases on carrier recovery. An iterative phase recovery method based on Turbo principle was performed, which outperforms the traditional methods. A carrier frequency estimation method was proposed, which can effectively control the fluctuation of the rudimental frequency brought by the conventional estimator and get better performance of FER(frame error rate) and BER(bit error rate), compared with the classical estimator.3. The equalization scheme was realized. In HF communication the intersymbol interference (ISI) is serious and is the main obstacle of HF high rate communication. So we must use the channel equalization technology to eliminate the influence of ISI if we want to improve the communication rate over certain BER. We performed the Turbo equalization and applied SIC(Soft Interference Canceller) algorithm to BICM-ID based on hard decision and improved its performance by making use of two methods: Firstly, we used the priori probability of transmitted signal as input on the first iteration and improved the performance of equalization, compared with the traditional method which uses the uniform probability distribution as input on the first iteration. Secondly, we combined SIC with MAP and proposed a combined MAP-SIC algorithm, which applied the MAP equalization algorithm to get more precise priori probability of transmitted signal on the first iteration. It outperformed the conventional SIC algorithm. We also performed the Turbo equalization in BICM-ID based on soft decision and proposed an improved iterative detection method based on the exchange of weighed extrinsic information probability, which can control the bit probabilities with large dynamics effectively and improve the system performance.4. The channel estimation scheme was realized.Turbo equalization is based on the hypothesis of the known channel parameters. In actual application, Channel Impulse Response and SNR are unknown, so we have to use the channel estimation technology to estimate these parameters. We proposed a semi-blind channel estimation algorithm in BICM system, which makes use of the decision information provided by the decoder and gets good channel estimation by iteratively exchanging information between the channel estimator and the decoder. This method works well with rough initialization of channel parameters obtained from very short train sequence, which leads to high spectrum efficiency.